Waterborne sub-lethal exposure to perfluorobutanesulfonate causes intestinal dysbiosis in tadpoles of Lithobates catesbeianus

Perfluorobutanesulfonate (PFBS) is a ubiquitous pollutant in the aquatic environment, but its toxic effects and mechanisms on amphibian species remain largely unknown. In the present study, tadpoles (Lithobates catesbeianus) were exposed to various concentrations of PFBS (0, 1, 3, 10, and 30 ​μg/L) for 14 days, with the goal of unveiling the impairment of intestinal health. Histopathological examination showed that sub-lethal exposure of tadpoles to PFBS at concentrations as low as 3 ​μg/L could result in the injury of intestinal structures. In a clear concentration-dependent manner, the expressions of epithelial barrier components (i.e., Claudin 1 gene and tight junction protein 2) were significantly decreased in PFBS-exposed intestines, while the intestinal content of lipopolysaccharide (LPS) and transcriptions of downstream responsive genes (e.g., TLR4, MyD88, and NF-κB) were concurrently significantly increased by exposure to 3, 10, and 30 ​μg/L of PFBS. As a consequence, the number of eosinophils and expression of pro-inflammatory cytokines (e.g., IL-1β and TNF-α) were increased therein. Furthermore, PFBS exposure induced oxidative stress in intestinal tissues by increasing the level of reactive oxygen species (ROS) and suppressing antioxidant capacity. The transcriptional levels of CytoC and Bax genes as well as activities of caspase 9 and caspase 3 enzymes were remarkably increased, while the transcript abundance of Bcl-2 was down-regulated significantly after PFBS exposure, thereby favoring apoptosis in tadpole intestines. PFBS sub-lethal exposure also drove the composition of intestinal microbiota to a dysbiosis status. Correlation analysis further revealed that the relative abundance of members of the genus Bosea was positively related with the contents of LPS and IL-1β. Overall, the present study provides the first evidence for pronounced impacts of PFBS on amphibian intestinal ecology, highlighting the susceptibility of tadpoles to the environmental risks of PFBS.